Unconventional oil is petroleum produced or extracted using techniques other than the natural mechanisms relied on by conventional methods. Oil industries and governments across the globe are investing in unconventional oil sources due to the depletion of conventional oil reserves.
Horizontal drilling and stimulations known as “fracking” have become increasingly important to the oil industry in recent years, especially for unconventional oil recovery. While horizontal wells have been drilled for many years, only recently have the link between this type of well and fracking (fracturing rock by pumping large volumes of proppant to create permeability, channels where the oil and gas can flow) provided a cost-effective alternative to conventional vertical well drilling. Although drilling a horizontal well costs substantially more than its vertical counterpart, a horizontal well frequently improves production by a factor of five, ten or even twenty in naturally-fractured reservoirs. Generally, projected productivity from a horizontal wellbore must triple that of a vertical wellbore for horizontal drilling to be economical. This increased production maximizes the return on investment.
Horizontal drilling makes reservoirs in urban areas, permafrost zones and deep offshore waters more accessible. Other applications for horizontal wellbores include periphery wells, thin reservoirs that would require too many vertical wellbores, and reservoirs with coning problems in which a horizontal wellbore could be optimally distanced from the fluid contact.
Some horizontal wellbores contain additional wellbores extending laterally from the primary vertical wellbores. Vertical wellbores containing more than one lateral wellbore are referred to as “multilateral” wells. Since the 1980s, multilateral wells are becoming increasingly important, both from the standpoint of new drilling operations and from the increasingly important standpoint of reworking existing wellbores, including remedial and stimulation work.
To reduce environmental impact at the surface and for economic reasons, many wells employ a single vertical mother wellbore having one or more multilateral junctions. The multilateral junctions allow multiple lateral wells to extend from the mother wellbore beneath the surface, which may increase oil recovery while reducing costs.
There exists a need for improved multilateral drilling techniques to increase oil production and reduce cost. Ideally, the method allows for the maximum number of laterals for a given pay potential, yet still minimize surface impact.